On 12/11/13 09:31, Mark Rogers wrote:
750 VA means it can deliver 250V at 3A
*if* everything connected has a power factor of 1 which is unlikely
As a guide.
A SMPSU with no power factor correction (anything cheap and under 75W this is quite likely) bet on a power factor of .5 to .6
A SMPSU with basic PFC is maybe .75
The very best Active PFC SMPSU's are about .9 (+85 spec PC power supplies and anything over 75W with the most recent Energy star rating is a good bet)
Just to confuse matters more even with PFC it is only designed to be optimal at 100% load as that is what is measured.
Short version, plugged into a selection of PC kit you should expect to get an average Power factor of around .75 so only 75% of that VA is turned into usable energy when converting to Watts or Amps.
As others have said VA rating has nothing to do with battery life..there is no time factor in a VA measurement so how can it. It's just coincidence that the larger models happen to have larger batteries so for the same load you'll get more runtime, but it's possible to buy 1500VA UPS's with different runtimes.